Panels of monoclonal antibodies (MAbs) to different forms of cytochrome P-450 have been used to identify the class of P-450 that is responsible for the catalysis of several different drug and carcinogen reactions. These include aryl hydrocarbon hydroxylase (AHH), ethoxycoumarin deethylase (ECD) and ethyl morphine deethylase (EMD) and benzphetamine demethylase (BPD). Several of the MAbs inhibit these reactions to different extents in the tissues of different species and strains of rodents. These MAbs can thus be used to prepare an atlas of P-450s responsible for various drug and carcinogen reactions in different tissues, strains and species. This approach represents a general method of phenotyping individuals for multi-enzyme systems.